1. Field of the Invention
The present invention relates generally to medical devices, and more particularly to an ultrasonic medical device for destroying tissue in a controlled fashion within a human body.
2. Description of Related Art
Medical instruments utilizing ultrasonic energy to destroy tissue in a human body are known in the art. One drawback of existing ultrasonic medical instruments which remove tissue is that typically doctors have considered them to be slow in comparison to methods such as surgical excision. Part of the reason for this perceived slowness is explained by the fact that most existing ultrasonic devices rely on a longitudinal vibration of the tip of the probe. In other words, the tip of the probe is vibrated in a direction in line with the longitudinal axis of the probe. This produces a tissue destroying affect only at the tip of the probe.
One solution that has been proposed is to vibrate the tip of the probe in a transverse directionxe2x80x94i.e. perpendicular to the longitudinal axis of the probexe2x80x94in addition to vibrating the tip in the longitudinal direction. For example, U.S. Pat. No. 4,961,424 to Kubota et al. discloses an ultrasonic treatment device to destroy and emulsify concretions or tissue in a human body. The Kubota et al. device produces both a longitudinal and transverse motion at the tip of the probe. The Kubota et al. patent, however, still relies solely on the tip of the probe to act as a working surface. Therefore, it improves the efficiency of the tip, but still relies on the tip of the probe to perform all cutting actions.
Although Kubota et al. describe providing a transverse motion at the tip of the probe, a transverse motion along the length of the probe has generally been discouraged. For example, U.S. Pat. No. 4,474,180 to Angulo discloses an ultrasonic kidney stone disintegration instrument with a damping material applied to the wire probe to inhibit lateral vibrations of the wire in the region of the connection to the ultrasonic transducer.
Another proposed method of improving the speed of ultrasonic tissue remove is oscillating the tip of the probe in addition to longitudinally vibrating the tip of the probe. For example, U.S. Pat. No. 4,504,264 to Kelman discloses an ultrasonic treatment device which improves the speed of ultrasonic tissue removal. In the Kelman device, the tip of the probe is vibrated longitudinally and also oscillated, so that the cutting efficiency of the probe tip is improved. Again, however, only the tip of the probe performs a cutting action.
The object of the present invention is to provide an ultrasonic medical device capable of destroying and emulsifying tissue through cavitation in the human body with a higher efficiency by means of a flexible probe operating in a transverse mode. As used herein, a transverse mode of operation is used to describe a flexible probe with a plurality of nodes and anti-nodes along the length of the probe.
In accordance with this object, an ultrasonic medical device comprises an ultrasonic vibration generator that generates vibration along its longitudinal axis. The ultrasonic vibration is transmitted through an ultrasonic coupler and a series of transformer sections that amplify the ultrasonic vibration. A flexible member is coupled to the distal end of the transformer sections, and is thus supplied with a longitudinal vibration at its base by the transformer sections. The flexible member is designed so that it converts the longitudinal vibration into a standing wave that runs along the length of the flexible member. The standing wave produces a series of nodes and anti-nodes along the length of the flexible member. Each of the anti-nodes produces cavitation in fluids in contact with the probe. The cavitation of the fluids causes destruction of adjacent tissue. Thus, in this manner, the entire length of the flexible member becomes a working surface that may be utilized for destroying tissue.
Therefore, in contrast to the prior art designs that only utilize a tip of a probe as a surface, the entire length of the flexible member forms a cutting surface in the present invention.